Ziegler-Natta catalyst systems are commonly used for polymerization of alpha-olefins.
U.S. Pat. No. 3,732,198 (Whiteley) concerns a method of polymerizing ethylene, at high pressure and temperature, employing a Ziegler-Natta catalyst pretreated with an allylic compound. The reference teaches the use of the allylic compound to suppress free radical polymerization and thereby suppress branching in the resulting polymer.
Kissin, Isospecific Polymerization of Olefins with Heterogeneous Ziegler-Natta Catalysts, pp. 185-188 (1985, Springer-Verlag N.Y., Inc.), concerns the addition of acetylene and allene to a Ziegler-Natta reaction mixture to halt polymerization of alpha-olefins. The reference reports that these are polymerizable additives, and therefore long runs of polyacetylene or polyallene are incorporated into the polymer chain. Once the acetylene and/or allene are consumed, polymerization of alpha-olefins resumes at the original rate.